The easiest way to hook up an aftermarket car stereo is to look at scheme car stereo connection for a specific vehicle and head unit, but it is actually possible to get the job done without any labels, adapters, or diagrams.

The reason you usually don’t need a wiring diagram to install a car stereo, even if it’s a used unit with no paperwork, is because the colors of wired car stereo wires are actually quite uniform. Unlike regular head units that are all over the place in terms of wire color, there is actually a standardized paint scheme that most aftermarket manufacturers follow.

Installing a used car stereo with or without pigtail

If you find yourself wanting to install a used car stereo and you have the pigtail that came with head unit then it’s usually just a process of checking the list in the next section of this article to see what each wire in the pigtail needs to connect.

If you don’t have a pigtail, your best bet would be to look for an adapter specifically designed to connect your head unit to your car make and model. If it doesn’t, you’ll still have to purchase a spare pigtail, and hopefully the colors these wires will meet the aftermarket standard.

Otherwise, you will need a wiring diagram, which is sometimes printed on the outside of the head unit or available online.

Standard aftermarket car stereo equipment

Illustration of a man looking at a wiring harness.
Lifewire / Nusha Ashjaee

While there are exceptions to every rule, most aftermarket car stereos use a standardized paint scheme for wires power supply, grounding, antennas and speakers. If you have the pigtail that came with the aftermarket head unit and it uses the standard colors, then the wires will have the following purposes and colors:

Power wires

  • Constant 12V / memory keep alive: yellow
  • Accessory: red
  • Dimmer / backlight: orange with white stripe

ground wires

  • Base: black


  • Right front speaker (+): gray
  • Right front speaker (-): gray with black stripe
  • Left front speaker (+): white
  • Left front speaker (-): white with black stripe
  • Right rear speaker (+): purple
  • Right rear speaker (-): purple with black stripe
  • Left Rear Speaker (+): Green
  • Left rear speaker (-): green with black stripe

Amplifier and antenna wires

  • Antenna: Blue
  • Remote turn-on amplifier: blue with white stripe

Using the Head Unit Harness Adapter

While most aftermarket head units follow the paint scheme above and it’s possible to figure out what all the OEM wires in your car are for without a wiring diagram, installing an aftermarket head unit is much easier if you have a harness adapter.

The reason car stereo harness adapters are so useful is because while aftermarket car stereos have all the same inputs and outputs as the factory stereos they are designed to replace, those inputs and outputs are not in the same places. .

If you manage to get a suitable wired stereo car adapter, it will make the installation process much easier. One end of the adapter connects to car stereo and the other to the wiring harness that was originally connected to the factory stereo, and that’s all there is to it.

Why doesn’t everyone use harness adapters instead of wire splices?

The problem is that while harness adapters are fairly inexpensive and available for a wide variety of car and head unit combinations, there really isn’t any wiggle room in terms of compatibility. For the head unit wiring harness to work, it must be specifically designed for both your vehicle and your new head unit.

If you can find out the specific model of head unit you trying to install there are online resources where you can plug them in along with the make, model and year of your vehicle to see if an adapter is available.

What if the Head Unit Harness Adapter is not available?

If you can’t figure out the specific model of head unit you’re using, then you’re better off determining the purpose of each wire and just manually connecting everything correctly.

In the same vein, there is also the possibility that there simply won’t be an adapter for any combination of car and head unit. If this is the case, and you also don’t have the pigtail that came with the head unit, then you’ll either have to get your hands on a replacement pigtail or go through the process of tracking the wiring. diagram and connection to individual contacts on the back of the head unit.

Although it is technically possible install head unit without wiring harness it is much more complicated than the basic head unit installation process, which suits most professionals.

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